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<head>
   <title>Apache Lucene API</title>
</head>
<body>

<p>Apache Lucene is a high-performance, full-featured text search engine library.
Here's a simple example how to use Lucene for indexing and searching (using JUnit
to check if the results are what we expect):</p>

<!-- code comes from org.apache.lucene.TestDemo: -->
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<pre class="prettyprint">
    Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_CURRENT);

    // Store the index in memory:
    Directory directory = new RAMDirectory();
    // To store an index on disk, use this instead:
    //Directory directory = FSDirectory.open("/tmp/testindex");
    IndexWriter iwriter = new IndexWriter(directory, analyzer, true,
                                          new IndexWriter.MaxFieldLength(25000));
    Document doc = new Document();
    String text = "This is the text to be indexed.";
    doc.add(new Field("fieldname", text, Field.Store.YES,
        Field.Index.ANALYZED));
    iwriter.addDocument(doc);
    iwriter.close();
    
    // Now search the index:
    IndexReader ireader = IndexReader.open(directory); // read-only=true
    IndexSearcher isearcher = new IndexSearcher(ireader);
    // Parse a simple query that searches for "text":
    QueryParser parser = new QueryParser("fieldname", analyzer);
    Query query = parser.parse("text");
    ScoreDoc[] hits = isearcher.search(query, null, 1000).scoreDocs;
    assertEquals(1, hits.length);
    // Iterate through the results:
    for (int i = 0; i < hits.length; i++) {
      Document hitDoc = isearcher.doc(hits[i].doc);
      assertEquals("This is the text to be indexed.", hitDoc.get("fieldname"));
    }
    isearcher.close();
    ireader.close();
    directory.close();</pre>
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<p>The Lucene API is divided into several packages:</p>

<ul>
<li>
<b><a href="org/apache/lucene/analysis/package-summary.html">org.apache.lucene.analysis</a></b>
defines an abstract <a href="org/apache/lucene/analysis/Analyzer.html">Analyzer</a>
API for converting text from a <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/io/Reader.html">java.io.Reader</a>
into a <a href="org/apache/lucene/analysis/TokenStream.html">TokenStream</a>,
an enumeration of token <a href="org/apache/lucene/util/Attribute.html">Attribute</a>s.&nbsp;
A TokenStream can be composed by applying <a href="org/apache/lucene/analysis/TokenFilter.html">TokenFilter</a>s
to the output of a <a href="org/apache/lucene/analysis/Tokenizer.html">Tokenizer</a>.&nbsp;
Tokenizers and TokenFilters are strung together and applied with an <a href="org/apache/lucene/analysis/Analyzer.html">Analyzer</a>.&nbsp;
A handful of Analyzer implementations are provided, including <a href="org/apache/lucene/analysis/StopAnalyzer.html">StopAnalyzer</a>
and the grammar-based <a href="org/apache/lucene/analysis/standard/StandardAnalyzer.html">StandardAnalyzer</a>.</li>

<li>
<b><a href="org/apache/lucene/document/package-summary.html">org.apache.lucene.document</a></b>
provides a simple <a href="org/apache/lucene/document/Document.html">Document</a>
class.&nbsp; A Document is simply a set of named <a href="org/apache/lucene/document/Field.html">Field</a>s,
whose values may be strings or instances of <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/io/Reader.html">java.io.Reader</a>.</li>

<li>
<b><a href="org/apache/lucene/index/package-summary.html">org.apache.lucene.index</a></b>
provides two primary classes: <a href="org/apache/lucene/index/IndexWriter.html">IndexWriter</a>,
which creates and adds documents to indices; and <a href="org/apache/lucene/index/IndexReader.html">IndexReader</a>,
which accesses the data in the index.</li>

<li>
<b><a href="org/apache/lucene/search/package-summary.html">org.apache.lucene.search</a></b>
provides data structures to represent queries (ie <a href="org/apache/lucene/search/TermQuery.html">TermQuery</a>
for individual words, <a href="org/apache/lucene/search/PhraseQuery.html">PhraseQuery</a>
for phrases, and <a href="org/apache/lucene/search/BooleanQuery.html">BooleanQuery</a>
for boolean combinations of queries) and the abstract <a href="org/apache/lucene/search/Searcher.html">Searcher</a>
which turns queries into <a href="org/apache/lucene/search/TopDocs.html">TopDocs</a>.
<a href="org/apache/lucene/search/IndexSearcher.html">IndexSearcher</a>
implements search over a single IndexReader.</li>

<li>
<b><a href="org/apache/lucene/queryParser/package-summary.html">org.apache.lucene.queryParser</a></b>
uses <a href="http://javacc.dev.java.net">JavaCC</a> to implement a
<a href="org/apache/lucene/queryParser/QueryParser.html">QueryParser</a>.</li>

<li>
<b><a href="org/apache/lucene/store/package-summary.html">org.apache.lucene.store</a></b>
defines an abstract class for storing persistent data, the <a href="org/apache/lucene/store/Directory.html">Directory</a>,
which is a collection of named files written by an <a href="org/apache/lucene/store/IndexOutput.html">IndexOutput</a>
and read by an <a href="org/apache/lucene/store/IndexInput.html">IndexInput</a>.&nbsp;
Multiple implementations are provided, including <a href="org/apache/lucene/store/FSDirectory.html">FSDirectory</a>,
which uses a file system directory to store files, and <a href="org/apache/lucene/store/RAMDirectory.html">RAMDirectory</a>
which implements files as memory-resident data structures.</li>

<li>
<b><a href="org/apache/lucene/util/package-summary.html">org.apache.lucene.util</a></b>
contains a few handy data structures and util classes, ie <a href="org/apache/lucene/util/BitVector.html">BitVector</a>
and <a href="org/apache/lucene/util/PriorityQueue.html">PriorityQueue</a>.</li>
</ul>
To use Lucene, an application should:
<ol>
<li>
Create <a href="org/apache/lucene/document/Document.html">Document</a>s by
adding
<a href="org/apache/lucene/document/Field.html">Field</a>s;</li>

<li>
Create an <a href="org/apache/lucene/index/IndexWriter.html">IndexWriter</a>
and add documents to it with <a href="org/apache/lucene/index/IndexWriter.html#addDocument(org.apache.lucene.document.Document)">addDocument()</a>;</li>

<li>
Call <a href="org/apache/lucene/queryParser/QueryParser.html#parse(java.lang.String)">QueryParser.parse()</a>
to build a query from a string; and</li>

<li>
Create an <a href="org/apache/lucene/search/IndexSearcher.html">IndexSearcher</a>
and pass the query to its <a href="org/apache/lucene/search/Searcher.html#search(org.apache.lucene.search.Query)">search()</a>
method.</li>
</ol>
Some simple examples of code which does this are:
<ul>
<li>
&nbsp;<a href="http://svn.apache.org/repos/asf/lucene/dev/branches/branch_3x/lucene/contrib/demo/src/java/org/apache/lucene/demo/IndexFiles.java">IndexFiles.java</a> creates an
index for all the files contained in a directory.</li>

<li>
&nbsp;<a href="http://svn.apache.org/repos/asf/lucene/dev/branches/branch_3x/lucene/demo/src/java/org/apache/lucene/demo/SearchFiles.java">SearchFiles.java</a> prompts for
queries and searches an index.</li>
</ul>
To demonstrate these, try something like:
<blockquote><tt>> <b>java -cp lucene.jar:lucene-demo.jar:lucene-analyzers-common.jar org.apache.lucene.demo.IndexFiles rec.food.recipes/soups</b></tt>
<br><tt>adding rec.food.recipes/soups/abalone-chowder</tt>
<br><tt>&nbsp; </tt>[ ... ]

<p><tt>> <b>java -cp lucene.jar:lucene-demo.jar:lucene-analyzers-common.jar org.apache.lucene.demo.SearchFiles</b></tt>
<br><tt>Query: <b>chowder</b></tt>
<br><tt>Searching for: chowder</tt>
<br><tt>34 total matching documents</tt>
<br><tt>1. rec.food.recipes/soups/spam-chowder</tt>
<br><tt>&nbsp; </tt>[ ... thirty-four documents contain the word "chowder" ... ]

<p><tt>Query: <b>"clam chowder" AND Manhattan</b></tt>
<br><tt>Searching for: +"clam chowder" +manhattan</tt>
<br><tt>2 total matching documents</tt>
<br><tt>1. rec.food.recipes/soups/clam-chowder</tt>
<br><tt>&nbsp; </tt>[ ... two documents contain the phrase "clam chowder"
and the word "manhattan" ... ]
<br>&nbsp;&nbsp;&nbsp; [ Note: "+" and "-" are canonical, but "AND", "OR"
and "NOT" may be used. ]</blockquote>

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